The term "bonded" refers to the state of being physically and rather permanently fastened together such as caused when polymers are melted and fused together.
The terms "fiber" or "fibers" refer to a pliable, cohesive, threadlike object or objects having a length to width ratio exceeding 100 to 1.
The terms "filament" or "filaments" refer to fiber or fibers having extreme or indefinite length.
The terms "continuous filament" or "continuous filaments" refer to a filament or filaments that have not been intentionally cut or broken.
The terms "staple fiber" or "staple fibers" refer to fibers cut to approximately 1-6 inch lengths.
The term "spreading" refers to the behavior of a yarn that is subjected to appropriate conditions (e.g., an attenuated air flow or static charge) so that the yarn separates into individual filaments. Spreading typically occurs most readily on yarns having low twist (less than 1 twist per inch), low crimp, low entanglement and low interfiber cohesion.
The term "web" refers to a fabric-like substantially planar (two-dimensional) arrangement of filaments.
The term "spun-bonded" refers to nonwoven fabrics formed by filaments that have been extruded, dram, then laid on a continuous belt to form a web. Bonding can be accomplished by several methods such as by hot roll calendering of the web or by passing the web through a saturated-steam chamber at an elevated pressure.
The term "monofilament" is any single filament of a manufactured fiber, usually of a denier higher than 20. Instead of a group of filaments being extruded through a spinneret to form a yarn, monofilaments generally (but not essentially) are spun individually. Monofilaments can be used for textiles such as hosiery or sewing thread or for nontextile uses such as bristles, papermaker's felts, fishing lines, etc.
The term "thermoplastic" is used to describe a plastic material that is permanently fusible.
The term "pulled reinforcement fibers" refers to fibers that extend more than 1 cm. from the fabric into the tear after a fabric is torn using ASTM D 2261-83. When more than three fibers of the reinforcement have been pulled out from the fabric such a condition indicates that the reinforcement yarn is not tightly bonded in the fabric and is able to spread the force at the propagation point of the tear over a larger area of the fabric than possible if the reinforcement is tightly bound. The term "pulled reinforcement fibers" does not apply in the case of delamination, which is the separation of layers of fabric parallel to the fabric surface.
Nonwoven web materials are known and find utility in a great variety of products including filters, scouring materials, abrasive carriers and carpet backing, as well as many other applications. Nonwoven webs made from continuous filaments have been described. For example, U.S. Pat. No. 3,616,160 to Wincklhofer et al. describes nonwoven webs formed from multiconstituent filaments. "Multiconstituent filaments" are defined as made by the inclusion of at least one polymeric material in a matrix of another by discontinuous fibrils. The materials have substantially different melting points. Such a structure is described as creating tongue tear strength up to 14.8 lbs. The multiconstituent filaments may be laid down with other types of filaments.
For many applications of nonwoven fabrics, including use as a carpet backing, a lingering obstacle has been how to provide sufficiently high tear strength. Many methods for improving the tear strength of nonwovens have been proposed. U.S. Pat. No. 3,607,359 to Bischoff et al. describes impregnating a nonwoven fabric with a low temperature latex bonding agent. This method is taught as increasing tear strength 35 to 50 percent higher than tear strength of nonwoven fabrics made prior to the patent. Specific tear strength values are not specified.
U.S. Pat. No. 3,652,353 to Belisle et al. discloses a multilayered laminate and describes a process for gluing staple fibers to a nonwoven web to impart improved tear strength. The stated rationale for the improved tear strength is the angular disposition of the fibers in the respective layers. That is, when the fibers are disposed substantially perpendicular to each other, the tear strength characteristics increase because tearing the laminate in any direction requires the breaking of fibers rather than merely spreading them apart. No strength values are reported.
U.S. Pat. No, 3,819,462 to Starr et al. discloses a nonwoven made from a base web formed from short length fibers (staple fibers) having continuous filaments stitched on the web in a tricot pattern. This web is described as useful for a tufted carpet primary backing. Two different deniers of staple fibers are used. The coarsest fibers are in the range of 6 to 20 denier per filament. The fine fibers have deniers of up to about 3 denier per filament. A 70 denier continuous multifilament polyester thread was used for the tricot pattern stitching. No strength values are reported.
U.S. Pat. No. 4,107,364 to Sisson discloses a drapeable nonwoven fabric. This fabric is made from at least one, and preferably at least two, separate streams of monofilaments of one or more fiber-forming synthetic organic polymers which are melt spun through one or more linear dyes or spinnerets from one or more extruders and laid down to form a nonwoven web. Prior to lay down, all the filaments are mechanically drawn to a textile denier (1 to 15 denier per filament).
U.S. Pat. No. 4,211,816 to Booker et al. describes the use of 10 to 20 denier per filament continuous heterofilaments to make a nonwoven web. These heterofilaments are made of at least two fiber-forming synthetic polymer components arranged in a sheath/core manner with the core being isotactic polypropylene and the sheath being high density polyethylene. Homofilaments may also be present in these fabrics in an amount of up to 30 weight percent. The filaments preferably have deniers in the range of 10 to 20. Elmendorf tear strength of at least 6 lb and normalized grab tensile strength of at least 120 are reported.
U.S. Pat. No. 4,921,659 to Marshall et al. describes a web formed by feeding separate supplies of long and short staple fibers. No strength data is provided.
U.S. Pat. No. 5,133,835 to Goettmann et al. describes a nonwoven composite web made of a blend of two or three different types of staple fibers having different lengths and different deniers. The maximum denier reported is 15. This web is described as providing a high tensile strength paper-like web.
There remains a need for high tear strength nonwoven materials for particular applications as tufting substrates, especially carpet tufting substrates. For example, for certain automotive carpets, the tufting substrate must consistently have tongue tear of at least 15 lbs as measured by ASTM D 2261-83 applied to nonwovens.